The present invention relates to magnetohydrodynamic power generation, and more particularly, to a unique diffuser design allowing steam generation within its walls.
In a magnetohydrodynamic (MHD) power generator, a diffuser is typically disposed downstream of the MHD generation channel to slow the high velocity gases exhausted therefrom prior to their submission to downstream generating equipment. The diffuser comprises a divergent open-ended duct, the cross-sectional area of the duct increasing continuously from the gas inlet end to the gas outlet end thereof. By passing high velocity gases through a diffuser, the gases are slowed so as to permit pressure recovery in accordance with the well-known Bernoulli's equation and temperature recovery in accordance with the well-known perfect gas law. In order to assure optimum pressure recovery, small half angles of divergence in the range of one to three degrees must be maintained when designing the diffuser.
Because of the high temperature of the gases passing from the MHD generation channel to the diffuser, approximately 3700 F., the diffuser walls must be constructed of refractory protected water-cooled tubes. The fact that the walls of the diffuser diverge at such small angles creates cooling problems. For instance, if the waterwall tubes containing the cooling water are oriented along the length of the divergent channel, boiling would have to be avoided because steam blanketing would occur in those tubes which are directed downhill. As a consequence of the steam blanketing, the tubes would overheat and fail. Thus, such a system would require large amounts of sub-cooled water in order to insure that steaming did not occur within the water-cooled tubes.